Transmitting device, receiving device and method for establishing a wireless communication link

ABSTRACT

A method for establishing a wireless communication link between a first communication device having a beam antenna to be steered to different positions and a second communication device. The method includes transmitting a link request signal from the first communication device to the second communication device via the beam antenna. The link request signal includes information relating to a current position of the beam antenna. The method further includes obtaining, in case the link request signal is received in the second communication device, channel quality information representative of a current transmission path.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and is based upon and claims thebenefit of priority under 35 U.S.C. §120 for U.S. Ser. No. 11/865,366,filed Oct. 1, 2007, the entire contents of this application isincorporated herein by reference. U.S. Ser. No. 11/865,366 claims thebenefit of priority under 35 U.S.C. § 119 from European Application No.06 021 152.1, filed on Oct. 9, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention related to a transmitting device and a receivingdevice for a wireless communication system, as well as to a method forestablishing a wireless communication link between such a transmittingdevice and receiving device.

2. Discussion of the Background

The present invention is particularly directed to problems and solutionsassociated with the establishment of a communication link between atransmitting device and a receiving device for a wireless communicationsystem, in which at least the transmitting device comprises a narrowbeam antenna which can be steered to different positions in order totransmit and eventually receive signals in a wireless communicationsystem. The receiving device can either also have a narrow beam antennawhich can be steered to different positions or a wider beam or evenomni-directional antenna.

SUMMARY OF THE INVENTION

At a given moment when transmitting device starts to try to establish acommunication link with a receiving device, the narrow beam antenna ofthe transmitting device may be in anyone of the available positions. Forthis particular position of the narrow beam antenna of the transmittingdevice, the corresponding channel quality of the associated transmissionpath may not be sufficient for the receiving device to receive a linkrequest signal transmitted from the transmitting device. For example,there might be an obstacle blocking this specific transmission path orchannel quality might be decreased for other reasons. The transmittingdevice has to vary the position of the narrow beam antenna until aposition for the narrow beam antenna has been found which provides atransmission path and therefore a communication link of a sufficientlygood quality so that a communication with the receiving device can beestablished. The situation is even worse when both the transmittingdevice and the receiving device each comprise a narrow beam antennawhich can be steered to different positions. At the moment at which thetransmitting device tries to establish a communication with thereceiving device, both narrow beam antennas might be totally misalignedso that the receiving device might not even receive any signal. Both thereceiving device and the transmitting device then have to vary thepositions of the respective narrow beam antenna until a link requestsignal of the communication device reaches the receiving device via atransmission path with a sufficiently high channel quality.

The object of the present invention is now to provide a transmittingdevice, a receiving device and a method for establishing a wirelesscommunication link between a first communication device having a narrowbeam antenna adapted to be steered into different positions and a secondcommunication device, which enable the establishment of a communicationlink in a simple but effective and reliable manner.

The above object is achieved by a method for establishing a wirelesscommunication link between a first communication device having a narrowbeam antenna adapted to be steered into different positions and a secondcommunication device. The method according to the present inventioncomprises the steps of transmitting a link request signal from the firstcommunication device to the second communication device via said narrowbeam antenna, wherein said link request signal comprises informationrelating to a current position of the narrow bean antenna, andobtaining, in case said link request signal is received in said secondcommunication device, channel quality information representative of acurrent transmission path.

Advantageously, the narrow beam antenna is steered to differentpositions and link request signal is transmitted for each position, eachof the link request signals comprising information relating to therespective position of the narrow beam antenna via which it istransmitted. Hereby, a sequence of the different positions of the narrowbeam antenna is advantageously based on a predefined pattern. Hereby,the first communication device advantageously transmits informationabout the predefined pattern to said second communication device.

Further advantageously, a sequence of the different positions of thenarrow beam antenna is based on random pattern.

Further advantageously, the first communication device, aftertransmitting of each link request signal, keeps the narrow beam antennain the just used position in order to be able to receive an answersignal from a second communication device. Further advantageously, thesecond communication device, for each of said link request signalsreceived in the second communication device, obtains channel qualityinformation representative of the respective transmission path. Hereby,the second communication device, on the basis of the obtained channelquality information, advantageously determines a suitable transmissionpath for a communication link with said first communication device andsends a link confirmation signal comprising information relating to thecorresponding position of the narrow beam antenna of the firstcommunication device to said first communication device.

Further advantageously, the link request signal comprises a preamble,said preamble comprising the information relating to the currentposition of the narrow beam antenna.

The above object is further achieved by a transmission device fortransmitting signals in a wireless communication system according toclaim 10. The transmitting device according to the present inventioncomprises a narrow beam antenna adapted to be steered to differentpositions, an antenna steering means adapted to steer said narrow beamantenna into said different positions, signal generating means adaptedto generate a link request signal comprising information relating to acurrent position of the narrow beam antenna, and a transmitting meansadapted to transmit said link request signal to a receiving device viasaid narrow beam antenna.

Advantageously, the signal generating means is adapted to generate linkrequest signals comprising information relating to each position of thenarrow beam antenna, wherein, when said antenna steering means steerssaid narrow beam antenna to different positions, a link request signalis transmitted for each position, each of the link request signalscomprising information relating to the respective position of the narrowbeam antenna via which it is transmitted. Hereby, the antenna steeringmeans advantageously steers the narrow beam antenna to the differentpositions based on a predefined pattern. Hereby, the transmitting meansis advantageously adapted to transmit information about the predefinedpattern to a receiving device.

Alternatively, the antenna steering means is advantageously adapted tosteer the narrow beam antenna to the different positions based on arandom pattern.

Further advantageously, after transmission of each link request signalthe narrow beam antenna of the transmitting device is kept in the justused position in order to be able to receive and answer signal from areceiving device.

Further advantageously, the transmitting device comprises a receivingmeans adapted to receive, from a receiving device, a link confirmationsignal comprising information relating to a position of the narrow beamantenna which is to be used for a communication with said receivingdevice.

Further advantageously, the link request signal comprises a preamble,said preamble comprising the information relating to the currentposition of the narrow beam antenna.

The above object is further achieved by a receiving device for receivingsignals in a wireless communication system according to claim 18. Thereceiving device according to the present invention comprises anantenna, a receiving means adapted to receive signals via said antenna,and a channel quality determining means adapted to determine a channelquality from a receiving link request signal comprising informationrelating to a position of a narrow beam antenna of a transmittingdevice.

Advantageously, the channel determining means determines a channelquality for each link request signal received from a transmittingdevice, wherein a control means determines a suitable transmission pathfor a communication link with said transmission device and a signalgenerating means generates a link confirmation signal on the basis ofthe determined channel quality, said link confirmation signal comprisinginformation about the corresponding position of the narrow beam antennaof the transmitting device, wherein the link confirmation signal istransmitted to the transmitting device.

Advantageously, the antenna of the receiving device is a narrow beamantenna which is adapted to be steered to different positions by meansof an antenna steering means. The antenna steering means isadvantageously adapted to steer the narrow beam antenna into differentpositions based on a random pattern. Alternatively, the antenna steeringmeans is advantageously adapted to steer the narrow beam antenna intodifferent positions based on a predefined pattern.

The present invention therefore enables the establishment of acommunication link between a transmitting device and a receiving devicein a simple but very effective and reliable manner. Specifically, sincethe link request signal transmitted from the transmitting devicecomprises information relating to the currently used position of thenarrow beam antenna of the transmitting device, the receiving device, bydetermining the channel quality information for the receiving linkrequest signal, is able to process and store information linking therespective antenna beam positions of the transmitting device to therespective channel quality of the transmission path and, by providingthe transmitting device with corresponding information, to establish acommunication with a good and reliable transmission quality. On thebasis of the channel quality information obtained in the receivingdevice, the position of the narrow beam antenna of the transmittingdevice can therefore be steered to a position which is associated with atransmission path having a high or the best channel quality for thecommunication between the two devices. In addition, in case that thereceiving device also comprises a narrow beam antenna which can besteered to different positions, the receiving device can control thepositions of the narrow beam antenna of the transmitting device and itsown narrow beam antenna position so that a communication link with thebest channel quality is established. The present invention furtherenables a very quick link establishment as soon as one position of thenarrow beam antenna (or the narrow beam antennas) is found, whichensures a communication link with a sufficiently high channel quality,so that it is possible to start a link establishment protocolimmediately without further beam alignment optimisation, i.e. withouthaving to find the or one of the best communication links. Obviously,after establishment of a communication link, a better or even the bestcommunication link can be further searched by the transmitting and/orthe receiving device. The present invention further enables to build anantenna device and/or receiving device with a much simpler and smallerantenna module, since an antenna means with only a steerable narrow beamantenna can be implemented. It is not necessary to additionallyimplement an omni-directional or wider beam antenna module, whichsupports the establishment of a communication link in the beginning of acommunication. The present invention enables the quick and reliableestablishment of a communication link only with a steerable narrow beamantenna, so that the costs, the size and the complexity of thetransmitting device and/or the receiving device can be reduced. Further,because of the higher gain of a narrow beam antenna compared toomni-directional antennas or wider beam antennas, it is possible toincrease the link budget and to reduce the multipath fading effects inthe communication.

It is to be noted that the transmitting device, the receiving device aswell as the method for establishing a wireless communication linkaccording to the present invention may be adapted to operate in any kindof wireless communication system in which information data and the likeare transmitted in wireless signals over a short, a mid or a long range.The transmitting device and receiving device can be any kind of portableand/or stationary equipments, devices, means, elements which enable andare adapted to transmit and receive signals in a wireless communicationsystem. The narrow beam antenna which is comprised in the transmittingdevice of the present invention and eventually also in the receivingdevice of the present invention and can be any kind of antenna which hasone beam or radiation direction which is more predominant than otherbeam or radiation directions and may also be called a sharp beamantenna, directional antenna or the like, in contrast toomni-directional antennas in which every beam direction is more or lessequal. Further, the steering of the narrow beam antenna(s) can berealised by any possible technical implementation, e.g. by mechanicaland/or electrical steering, by changing gain and/or phase of antennaelements forming the narrow beam antenna, by individually controllingone or more antenna elements of the number of antenna elements formingthe narrow beam antenna or any other possible implementation.Advantageously, it should be assumed that the steering of the narrowbeam antenna takes place step by step and not continuously.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further explained in the following descriptionof preferred embodiments in relation to the enclosed drawings, in which

FIG. 1 schematically visualises the link establishment between atransmitting device and a receiving device,

FIG. 2 schematically shows a block diagram of a transmitting deviceaccording to the present invention,

FIG. 3 schematically shows a block diagram of a receiving device of thepresent invention,

FIG. 4 schematically shows the transmission of a number of link requestsignals from a transmitting device according to the present invention,

FIG. 5 schematically shows a link establishment procedure between atransmitting device and a receiving device of the present invention,

FIG. 6 schematically shows an example of scrambling of a link requestsignal, and

FIG. 7 schematically shows a further example of scrambling a linkrequest signal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically shows how a communication link between atransmitting device 1 and a receiving device 10 according to the presentinvention is established. The transmitting device 1 will be explained inmore detail in relation to FIG. 2. The receiving device 10 will beexplained in more detail in relation to FIG. 3.

The transmitting device 1 comprises a narrow beam antenna 2 which isadapted to be steered into different positions as shown in FIG. 1. Inthe example shown in FIG. 1, the receiving device 10 also has a narrowbeam antenna 11 which is adapted to be steered to different positions.However, according to the present invention, the receiving device 10 mayalso have a wide beam or omni-directional antenna, which cannot besteered to a predominant beam position. In the example shown in FIG. 1,the narrow beam antennas 2 and 11 can be steered to different positions,so that a number of different transmission paths T₁, T₂, T₃ and T₄between the transmitting device 10 are possible. In the shown example,one of the transmission paths, namely T₁, is blocked by an obstacle.This transmission path T₁ would also be the direct line of sighttransmission path between the transmitting device 1 and the receivingdevice 10. The narrow beam antennas 12 and 11 therefore have to besteered to respective positions in which the exchange of data and acommunication is possible. The transmission paths T₂, T₃ and T₄ whichare indirect (no line of sight) transmission paths in which thetransmitted signal is reflected towards the receiving device 10. FromFIG. 1 it becomes immediately clear that an essential problem is toalign the narrow beam antennas 2 and 11, i.e. to steer both antennasinto a respective positions which enables the communication.

FIG. 2 shows a schematic block diagram of a transmitting device 1according to the present invention. The transmitting device 1 is adaptedto transmit and receive signals in a wireless communication system andtherefore comprises all necessary elements and implementations in orderto be able to perform the necessary functionalities. However, for thesake of clarity, FIG. 2 only shows and explains elements which arenecessary for the understanding of the present invention. Further, it isto be noted that although the transmitting device 1 is called“transmitting device” throughout the present specification, it has to beunderstood that the transmitting device 1 is also adapted to receivesignals in the wireless communication system. However, since thetransmitting device 1 is a device which initiates the communication withthe receiving device 10 by transmitting a link request signal, which isthen answered by the receiving device 10, this wording was chosen.Similarly, the receiving device shown and explained in relation to FIG.3 is also adapted to transmit signals in the wireless communicationsystem. However, since the receiving device answers a link requestsignal received from the transmitting device 1 in order to establish acommunication, this wording was chosen. Further, the transmitting device1 could also comprise the elements and functionalities of the receivingdevice 10 and vice versa.

The transmitting device 1 comprises a narrow beam antenna 2 which isadapted to be steered to different positions by an antenna steeringmeans 4 under the control of a control means 5. The control means can beany kind of suitable control means, e.g. a base band control means ofthe transmitting device 1 or any other suitable control unit. Thetransmitting device 1 further comprises a transceiving means 3 adaptedto transmit and receive signals in a wireless communication system viathe narrow beam antenna 2. The transceiver 3 is e.g. implemented as thehigh frequency part or radio frequency part of the transmitting device1. The transmitting device 1 further comprises a signal generating means7 which is adapted to generate link request signals which are thentransmitted by the transceiver 3 via the narrow beam antenna 2 to thereceiving device 10. The term “link request signal” is hereby intendedto cover all kinds of possible signals which are initially transmittedfrom a transmitting device 1 in order to identify and/or signalise thepresence of the transmitting device 1, request the establishment of acommunication, and so forth, such as beacon signals and the like. Thelink request signals generated by the signal generating means 7respectively comprise information relating to a respective position ofthe narrow beam antenna. At the beginning of the link establishmentprocedure, the narrow beam antenna 2 is steered to or already in aspecific position and sends out a link request signal. This link requestsignal comprises information which relates to the current position ofthe narrow beam antenna 2. Information relating to a current positionhereby means that the information indicates in which position the narrowbeam antenna 2 was when the link request signal was transmitted. At thebeginning of the link establishment procedure, the antenna steeringmeans 4 steers the narrow beam antenna 2 to different positions, wherebyin each position a corresponding link request signal generated by thesignal generating means 7 comprising information about the respectiveposition of the narrow beam antenna 2 is transmitted. This procedure isvisualised in the upper line of FIG. 4 and the left side of FIG. 5. Inboth figures the link request signal is called “beacon signal”. Further,in both figures, the information relating to the current position of thenarrow beam antenna is called ANT_ID, i.e. an identification indicatingthe respective position and beam direction of the narrow beam antenna 2.As shown in the upper line of FIG. 4, the narrow beam antenna 2transmits a link request signal (or beacon signal) from various antennapositions, which are identified by ANT_ID=1, 2, 3 or 4. This sequence ofvarious antenna positions can either be a random sequence or apredefined sequence. In case that the sequence of varying narrow beamantenna positions is a predefined sequence, this information about thepredefined sequence could be transmitted to the receiving device 10 inorder to accelerate and support the link establishment procedure.

After the transmission of each link request or beacon signal, the narrowbeam antenna 2 remains in the same position for a certain time(listening time), as visualised in FIG. 4, during which an answer signalcan be received from a receiving device 10. Therefore, in case that areceiving device 10 received the link request signal, the receivingdevice 10, as will be explained below, can process the received linkrequest signal and send an answer signal (or link confirmation signal)back to the transmitting device 1.

A schematic block diagram of a receiving device 10 according to thepresent invention is shown in FIG. 3. Hereby, the receiving device 10comprises all necessary elements and functionalities in order to enablethe reception and transmission of signals in the wireless communicationsystem. However, for the sake of clarity, FIG. 3 only shows and explainsthe elements necessary for the understanding of the present invention.

The receiving device 10 comprises a narrow beam antenna 11 which can besteered to different positions by an antenna steering means 17 under thecontrol of the control means 13. The control means 13 can be a base bandcontroller of the receiving device 10 or any other suitable controllingunit. The control means 13 is connected or comprises a memory 14 inorder to store data, information, software, applications and so forth.The receiving device 10 further comprises a transceiver 12 adapted toreceive and transmit signals via the narrow beam antenna 11. Thetransceiver 12 is e.g. implemented as a high frequency or radiofrequency unit of the receiving device 10. The receiving device 10further comprises a channel estimator 15 which is adapted to estimate orobtain information about the channel quality of signals received via thenarrow beam antenna 11 and the transceiver 12. The obtained channelquality information is further processed by the control means 13. Thereceiving device 10 further comprises a signal detecting means 15 whichis adapted to detect a received link request signal and particularlyinformation relating to the position of the narrow beam antenna 2 of atransmitting device 1 comprised in a received link request signal. Thedetected information is then further processed in the control means 13.The receiving device 10 further comprises a signal generating means 18which is adapted to generate, under the control of the control means 13,the link confirmation signal to the transmitting device 1 from which alink request signal was received via the transceiver 12 and the narrowbeam antenna 11.

The link confirmation signal hereby comprises information about theposition of the narrow beam antenna of the transmitting device 1 fromwhich the corresponding link request signal was received. This is e.g.visualised in FIG. 4, while the transmitting device 1 transmits linkrequest signals from various positions of the narrow beam antenna 2, thereceiving device 10 also changes the position of the narrow beam antenna11 to various positions trying to listen or receive link request signals(beacon signals) by changing the antenna beam direction. When a linkrequest signal is received in the receiving device 10, the quality ofthe channel is determined in the channel estimator 15. In case that thechannel quality is good enough, the control means 13 causes thegeneration of a link confirmation signal in the signal generator 18which is transmitted back to the transmitting device 1, whereby the linkconfirmation signal comprises information about the position of thenarrow beam antenna 2 which was used to transmit the link requestsignal. This, as explained, takes place while the narrow beam antenna 2of the transmitting device 1 is still in the same position.

In FIG. 4, the information about the position of the narrow beam antenna2 which had a sufficient channel quality is named DESIRED_ANT_ID=1, i.e.signifying that the antenna position 1 of the narrow beam antenna 2 hada sufficient quality in the corresponding transmission path.Alternatively, instead of answering immediately as soon as a linkrequest signal over a transmission path with a sufficient channelquality is received in the receiving device 10, the receiving device 10could change the position of its narrow beam antenna 11 a predefinednumber of times trying to receive several link request signals, wherebyeach link request signal is evaluated in relation to the channelquality, whereafter the control means 13 of the receiving device 10selects the transmission path, i.e. the positions of the narrow beamantennas 2 and 10 associated with the transmission path with the besttransmission quality, for the communication link and sends correspondinginformation back to the transmitting device 1. The schematic example ofFIG. 4 explains the situation for a time division duplex system, inwhich the transmission and the reception of signals takes placesequentially. However, the present invention can also be applied to anyother transmission schemes, such as frequency division duplex and soforth.

FIG. 5 also visualises a link establishment procedure between thetransmitting device 1 and the receiving device 10. In a first step, thetransmitting device 1 is transmitting link request signals (beaconsignals) from different positions of the narrow beam antenna 2 accordingto a predefined or random pattern. At the same time, the receivingdevice 10 changes the position of the narrow beam antenna 11 also eitheron the basis of a random pattern or a predefined pattern attempting toreceive a link request signal from a transmitting device 1. In a secondstep, when the receiving device 10 has received one or more link requestsignals over a transmission path with a sufficient channel quality, alink confirmation signal (or connect request signal) is transmitted backto the transmitting device 1, the link confirmation signal comprisinginformation about the desired position of the narrow beam antenna 2 ofthe transmitting device 1 (DESIRED_ANT_ID). The transmitting device 1then, in a third step, acknowledges the requested communication link,whereafter a communication link is established in a fourth step. Asvisualised in a fifth step during the exchange of information, data andso forth over the established communication link, the transmittingdevice as well as the receiving device 10 may at certain times changethe position of the narrow beam antennas 2 and 11 in order to testalternative transmission paths in case that the current transmissionpath breaks down or deteriorates.

The structure of the link request signal generated by the signalgenerator 7 of the transmitting device 1 as well as the structure of thelink confirmation signal generated by a signal generator 18 of thereceiving device 10 ca be varied and adopted to the respective wirelesscommunication system. For example, as shown in FIG. 6, the link requestsignal and link confirmation signal may have a structure comprising apreamble, whereby the preamble comprises the information relating to thecurrent position of the narrow beam antenna 2. Eventually, a scramblingcode can be applied to the preamble part comprising the informationrelating to the current position of the narrow beam antenna. Hereby, thedata rate of the preamble can be slower than the data part of the linkrequest signal, which is eventually not scrambled. However, theinvention is also applicable for other signal structures, e.g, signalswithout scrambling, a signal in which the data part is also scrambled, asignal without data part and/or a signal which has the information aboutthe current position of the narrow beam antenna in the data part.

In the following, scrambling possibilities performed e.g. in the signalgenerating means 7 are explained. If the symbol duration of data part isdenoted as T, the chip duration of the scrambling code Tc must be T. Inthis example scrambling is applied on the preamble partTs=N Tc=NTwhere N is spreading factor and positive integer, and Ts is the symbolduration of the preamble part. If the spreading factor becomes bigger,the received signal to noise ratio (SNR) after descrambling in thereceiving device 10 becomes N times higher. The symbol duration of thepreamble part Ts becomes N times slower than the symbol rate of datapart. For the exchange of the antenna position information ANT_ID, it isnot necessary to have a high data rate.

The scrambling code is e.g. chosen as PN sequence which has impulse typeautocorrelation function.

Synchronization process based on the scrambled preamble.: As explainedabove, the autocorrelation function of the scrambling code has impulse(M sequence, Gold code etc.). Therefore by checking the position of thespike from the crosscorrelation between received preamble and knownscrambling code, it is possible to obtain timing synchronization in thereceiving device 10. Denote the scrambling code as c(t), preamble s(t),and channel h(t), the received signal can be expressed as follows;r(t)=c(t)s(t)h(t) t=t, . . . , t+(N−1)Tc

Then the signal after descrambling with timing synchronization becomesy(t)=c*(t)r(t)=N|c(t)|² s(t)h(t)where s(t) is known sequence and |c(t)|² is real constant. Therefore itis possible to estimate h(t), if s(t) is known.

In the following, the phase ambiguity is explained.

-   -   When s(t) has information like ANT_ID, the received signal can        be expressed        y _(p)(t)=c*(t)r _(p)(t)=N|c(t)|³ s _(p)(t)h(t)

Because s_(p)(t) has information, it's unknown. Assume that s_(p)(t)isQPSK, it has 4 states l, −l, j, −j. It causes phase ambiquity.

If we use differential QSPK to generate s_(p)(t), likep=s _(p)(t)s* _(p)(t−Ts)

-   -   The phase difference between two symbols shows information p,        and the phase ambiquity can be ignored.

In the following, the code generation is explained.

The example shown in FIG. 6 has ANT_ID scrambled with scrambling code.The ANT_ID is detected by descrambling the signal. Another idea is shownin FIG. 7, which has multiple layered scrambling codes. Each of primaryscrambling code and secondary code are PN sequence or orthogonal codes.For example primary scrambling code is kept for any signal, andsecondary scrambling code is selected depend on ANT_ID. In this case, bydetecting the secondary scrambling code, it is possible to get AND_ID.The data part could have other information, or keep constant value. Thisidea is also applicable on connection request signal and DESIRED_ANT_ID.

The terminology used in the present description is explained in thefollowing:

ANT_ID: An ID which indicates the beam direction or position of beamsteering antenna. It is assumed that the beam direction or position canbe changed step by step, not continuously.

Beacon: Signal transmitted from a radio station to show the existence ofthe radio station.

Preamble: Additional signal to the data part for the purpose of signaldetection, timing recovery, carrier recovery etc.

Beam alignment: The relative directions of the antenna beams. Forexample when the transmitter's beam is aiming to the receiver and thereceiver's beam is aming to the transmitter, one can say the beam arealigned.

Beam direction: Direction of the antenna beam.

Beam steering: To change the antenna beam direction.

Channel quality: A index showing the quality of the communicationchannel. For example if a preamble is chosen as PN sequence, the crosscorrelation value between received preamble part and its replica showsthe received signal strength and noise level. If the signal strength ismuch bigger than noise level, it can say that the channel quality ishigh.

Connection request signal: A signal to request establishing a link afterreceiving beacon signals.

DESIRED_ANT_ID: The ANT_ID which is desired and indicated from S2 to S1when it sends communication request signal. The DESIRED_ANT_ID is chosenbased on channel quality of received beacons.

Orthogonal code: A code which have zero cross-correlationi. For example,Walsh function.

The general idea of the present invention and some advantageousimplementations are again explained in the following. The general ideaof the present invention is to put antenna direction information ANT_IDon a link request or beacon signal in order to show ANT_ID currentlyused. Further advantageous implementation ideas and examples are totransmit said beacon signals with ANT_ID by changing beam directions foreach as shown in FIG. 4, to transmit a communication request or linkconfirmation signal with the desired beam direction informationDESIRED_ANT_ID, which is chosen besed on received said beacons withANT_ID. to keep the beam direction of the transmitter during “listeningtime” as shown in FIG. 4, to put ANT_ID information on preamble of saidbeacon signal and/or communication request signal, to apply scramblingon said beacon and/or connection request message with scrambling code inorder to have spreading gain. The following ideas can also beimplemented according to the present invention:

A wireless receiver which makes the synchronization process of carrierfrequency, phase and timing (or some of them) based on said preamble.

The antenna direction information ANT_ID is modulated as a differentialphase shift keying modulation or a differential code. It can avoid thephase ambiguity of modulation signal.

The signal has primary and secondary scrambling codes and the secondarycode is chosen depend on ANT_ID for beacon signal or DESIRED_ANT_ID forconnection request signal.

PN sequence or orthogonal code is used for the secondary scramblingcode.

The pattern of beam direction can be random, or predefined pattern.

The predefined pattern can be informed from the transmitter to thereceiver.

1. A method for establishing a wireless communication link between afirst communication device and a second communication device, said firstcommunication device having an antenna beam operable at differentpositions, the method comprising transmitting a link request signal fromsaid first communication device to said second communication device viasaid beam antenna beam, wherein said link request signal comprisesinformation relating to a current position of the antenna beam; andobtaining, in case said link request signal is received in said secondcommunication device, channel quality information representative of acurrent transmission path.
 2. The method according to claim 1, whereinsaid antenna beam is steered to different positions and a link requestsignal is transmitted for each position, each of the link requestsignals comprising information relating to the respective position ofsaid antenna beam via which it is transmitted.
 3. The method accordingto claim 2, wherein a sequence of the different positions of saidantenna beam is based on a predefined pattern.
 4. The method accordingto claim 3, wherein said first communication device transmitsinformation about said predefined pattern to said second communicationdevice.
 5. The method according to claim 2, wherein a sequence of thedifferent positions of said antenna beam is based on a random pattern.6. The method according to claim 2, wherein the first communicationdevice, after transmission of each link request signal, keeps theantenna beam in the just used position in order to be able to receive ananswer signal from a second communication device.
 7. The methodaccording to claim 2, wherein said second communication device, for eachof said link request signals received in said second communicationdevice, obtains channel quality information representative of therespective transmission path.
 8. The method according to claim 7,wherein said second communication device, on the basis of the obtainedchannel quality information, determines a suitable transmission path fora communication link with said first communication device and sends alink confirmation signal comprising information relating to thecorresponding position of the antenna beam of the first communicationdevice to said first communication device.
 9. The method according toclaim 1, wherein said link request signal comprises a preamble, saidpreamble comprising the information relating to the current position ofthe antenna beam.
 10. A transmitting device for transmitting signals ina wireless communication system, comprising an antenna beam operable atdifferent positions a signal generating unit configured to generate alink request signal comprising information relating to a currentposition of the antenna beam, and a transmitting unit configured totransmit said link request signal to a receiving device via said antennabeam.
 11. The transmitting device according to claim 10, wherein saidsignal generating unit is configured to generate link request signalscomprising information relating to each position of said antenna beam,wherein when an antenna steering unit steers said antenna beam todifferent positions, a link request signal is transmitted for eachposition, each of the link request signals comprising informationrelating to the respective position of said antenna beam via which it istransmitted.
 12. The transmitting device according to claim 11, whereinsaid antenna steering unit steers said antenna beam to the differentpositions based on a predefined pattern.
 13. The transmitting deviceaccording to claim 12, wherein said transmitting unit is configured totransmit information about said predefined pattern to a receivingdevice.
 14. The transmitting device according to claim 11, wherein saidantenna steering unit steers said antenna beam to the differentpositions based on a random pattern.
 15. The transmitting deviceaccording to claim 11, wherein, after transmission of each link requestsignal, the antenna beam is kept in the just used position in order tobe able to receive an answer signal from a receiving device.
 16. Thetransmitting device according to claim 10, further comprising; areceiving unit configured to receive from a receiving device a linkconfirmation signal comprising information relating to a position of theantenna beam which is to be used for a communication with said receivingdevice.
 17. The transmitting device according to claim 10, wherein saidlink request signal comprises a preamble, said preamble comprising theinformation relating to the current position of the antenna beam.